Limit apparatus

ABSTRACT

Limit apparatus including a housing having switch means mounted thereon and connected with drive means which is operative in response to a predetermined parameter exceeding a selected magnitude to close the switch means. A cutoff device is coupled with the switch means and includes a lever arm carried pivotally from the housing and biased to a cutoff positon holding said switch means open but normally maintained in an inoperative position by means of electromagnetic means which selectively attracts a ferromagnetic keeper carried on such lever arm to maintain such lever arm pivoted against the bias of such biasing means. Limit control means is connected in circuit with the electromagnetic means and is responsive to a selected parameter to de-energize such electromagnetic means to release the keeper to enable the lever arm to rotate under the influence of the biasing means to thus open the switch means.

United States Patent Teichert 1 5] Nov. 20, 1973 LIMIT APPARATUS PrimaryExaminer-Harold Broomc [75] Inventor: Allen L. Teichert, Placentia,Calif. Atwmey vem Schools) at [73] Assignee: Robertshaw ControlsCompany,

Richmond, Va. [57] ABSTRACT Limit apparatus including a housing havingswitch [22] 1972 means mounted thereon and connected with drive [21]Appl. No.: 301,302 means which is operative in response to apredetermined parameter exceeding a selected magnitude to close theswitch means. A cutoff device is coupled [52] ;g; f with the switchmeans and includes a lever arm car- 51 I t Cl 24 ried pivotally from thehousing and biased to a cutoff positon holding said switch means openbut normally 1 o g "I I l7 f maintained in an inoperative position bymeans of 3 ll 1 3 f electromagnetic means which selectively attracts afer- 3 l romagnetic keeper carried on such lever arm to maintain suchlever arm pivoted against the bias of such bi- [56] References cuedasing means. Limit control means is connected in cir- UNITED STATESPATENTS cuit with the electromagnetic means and is responsive 2,635,1544/1953 Zuckerman 335/126 to a selected parameter to de-energize suchelectro- 2,658,123 11/1953 SlOeSer 126 magnetic means to release thekeeper to enable the 3,109,906 11/1963 Abefldmth 335/l70 lever arm torotate under the influence of the biasing 3,648,204 3/1972 Davies et al.335/170 means to thus openthe Switch means 3,655,932 4/1972 Tabares etal. 200/5 C 10 Claims, 9 Drawing Figures 7 1 4 7 i I u I s4 if i 53 7577 54 5/ E O 52 l w U Q l Q Q 4 3i v 1 O I i w s .5 59 w a LIMITAPPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Thelimit apparatus of the present invention relates to a device foroverriding a switch control means to selectively open such switch.

2. Description of the Prior Art Applicant is unaware of any prior artlimit apparatuses which incorporate a pivotable lever arm biased to anoverride position engaging a switch means to open such switch means butnormally held in an operative position by means of an electromagnetwhich is connected in circuit with limit control means and is operativein response to sensing a selected parameter to deenergize such magnet. I

The objects and advantages of the present invention will become apparentfroma consideration of the following detailed description when taken inconjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are transverse sectionalviews of a limit apparatus embodying the present invention and depictingsuch apparatus in different modes of operation;

FIGS. 4, and 6 are longitudinal sectional views taken along the lines4-4, 5-5 and 6-6 of the respective FIGS. 1, 2 and 3; and

FIGS. 7, 8 and 9 are partial longitudinal sectional views taken alongthe respective lines 7-7, 8-8 and 9-9 of the respective FIGS. 1, 2 and3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The limit apparatus of thepresent invention includes, generally, a housing 11 having a pluralityof switches 13 mounted therein and opened by means of axially shiftabledrive camshaft 15 coupled with a drive linkage 19 which incorporates athermostatic control rod 21 that is selectively heated to effectshifting of such cam and closure of the respective switches. A cutoffcam bar 23 is disposed adjacent the drive camshaft 15 (FIG. 7) and hasone end thereof coupled with one end of a lever arm 27 included in acutoff device 25, such arm being biased counter-clockwise by means of atension spring 29 which urges such lever arm to the cutoff positionshown in FIG. 9. The opposite end of such lever arm 27 carries aferromagnetic keeper 33 which is disposed adjacent an electromagnet 35having a control switch 37 connected in circuit therewith. Consequently,when a predetermined parameter of a selected magnitude is sensed, thethermostatic rod control 21 will be heated to shift the drive camshaft15 to the left to enable the switches 13 to assume their closed positionshown in FIG. 2. However, sensing of a limit parameter will result inopening of the limit switch 37 thus de-energizing the electromagnet 35to free the lever arm 27 for rotation counter-clockwise'to the cutoffposition shown in FIG. 9 thus shifting the limit cam 23 axially to theleft to assume the position shown in FIG. 3 thus opening the respectiveswitches 13.

Referring to FIGS. 4 6, the switches 13 are formed by upstandngresilient electrically conductive blades 41 and 43 having respectiveelectrical contacts 45 and 47 mounted intermediately thereon and havetheir bases 2 projecting through the housing 11 to form respective plugprongs 49 and 51.

Referring to FIGS. 1, 7 and 4, the drive camshaft I3 is in the form of asemi-cylindrical shaft disposed between the free extremities of therespective switch blades 41 and 43 and formed with a plurality of dwellcams 52 axially therealong and each formed with wedge shaped camsurfaces 53, the symmetry of which provides for equal and oppositemovement of the respective free ends of the blades 41 and 43 as suchcamshaft 15 is shifted axially to the left from the figure shown in FIG.1 to the figure shown in FIG. 2 to thus permit the free extremitiesofsuch blades to move rapidly inwardly toward one another with equal andopposite speeds to thus bring the respective contacts 45 and 47 intocontact with one another at rates of equal and opposite speeds. The cams52 are separated by minor diameter necks 56 of a sufficiently smalldiameter to permit the blades 41 and 43 to bring the contacts 45 and 47together when disposed between such blades. In the preferred embodiment,the switches 13 are in- Referring to FIGS. 1 3, the drive camshaft 15 isformed on its right hand end with a side driver notch 51 which has thefree end of an upstanding drive link 53 included in the drive linkage 19disposed therein,

the opposite end of such link being mounted from a longitudinal mountingbracket 54 by means of a pivot pin 55. A secondary link 57 is mountedfrom the end of the mounting bracket 54 opposite the drive link 53 bymeans ofa pivot pin 59 and is arranged generally coextensive with thedrive link 53. The free end of the secondary link 57 is pivotallyconnected with the base of the drive link 53 by means ofa diagonal link61. The upper extremity of the drive line 53 is urged to the left bymeans ofa tension spring connected between the free extremities of thelinks 53 and 57. Leftward movement of the free extremity of thesecondary drive link 57 is controlled by means of the thermostatic rod21, such rod being anchored on one end to a flange 67 and the oppositeend of such rod projecting through a bore in the link 57 and having anut 71 screwed thereonto. The intermediate portion of the control rod 21is wrapped with a high resistance heat motor 72 which may be connectedin circuit with a control element such as a thermostat.

Referring to FIGS. 1, 2 and 7, the cutoff cam bar 23 is arranged overand projects coaxially with the drive camshaft 15, such camshaft beingformed with individual cams 75 which are formed on one end withoppositely disposed and oppositely angled cam surfaces 77 for engagementwith the respective switch blades 41 and 43 to urge the free extremitiesthereof apart. When the drive camshaft 15 is in its switch-closeposition shown in FIG. 2 and the cutoff cam bar 23 is in its inoperativeposition as shown in FIG. 2, the enlarged-indiameter drive and cutoffcams 52 and 75 of the respective camshaft and rod 15 and 23 are alignedwith one another so the minor diameters of the respective camshafts aredisposed between the respective blades 41 and 43 to permit the freeextremities of such blades to. move inwardly toward one another andcarry the contacts 45 and 47 into engagement with one another as shownin FIG. 5.

Referring to FIG. 7, the cutoff device 25 is coupled with the commonends of the respective drive and cutoff camshaft and rod 15 and 23, theupper extremity of the lever arm 27 being bifurcated to form a firstprong 81 received in a cutout 83 formed in the end of the drive camshaftl5 and abutting such shaft. The second prong 85 formed in, the upperextremity of such lever 27 is received in a downwardly opening slot 87formed in a downturned flange 88 at the right hand end of the cutoff cambar 23.

Referring to FIGS. 7 and 9, the lever arm 27 itself is carried in ahousing aperture 89 which forms a fulcrum. Mounted adjacent theintermediate portion of such lever arm 27 is a reset switch, generallydesignated 91, such switch including a stationary contact 93 and amovable contact 95. Still referring to FIG. 7, an upstanding mountingbracket 107 is affixedto the housing 11 and has an electrical insulator96 projecting therefrom to mount a pair of downwardly projectingelectrically conductive blades 97 and 99 which mount the contacts 93 and95 on the respective extremities thereof. The blade 99 is resilient andis formed to normally assume the bent position shown in FIG. 9maintaining the movable contact 95 spaced from the stationary contact93. The blades 97 and 99 of the reset switch 91 are connected in serieswith the thermostatic control rod 21 by means ofleads 101 and 103, thepurpose of such connection appearing hereinafter.

The electromagnet 35 is mounted from the mounting bracket 107 carried onthe housing 11 and has its coil connected in series with a switch 37formed by a thermostatic blade which is responsive to a predeterminedtemperature to open.

In operation, the limit apparatus of the present invention mayconveniently be utilized in a control system for controlling a furnaceto prevent overheating thereof. In such arrangements, the switches 13may be connected in circuit with respective heating elements of amultiple heating elementfurnace, it being appreciated that the switch 13shown at the far left in FIG. 1 may be connected with the blower of suchfurnace and that due to the staggered relationship of the cam elements52 with respect to the contact mounting blades 41 and 43, the switch 13will be the first switch closed as the drive camshaft 15 is shifted tothe left thus assuring energization of such blower prior to the time anyof the heating elements are energized to prevent overheating of suchelement before air is circulated thereover. Further, it will beappreciated that the cutoff cam bar 23 does not incorporate a cam 73 forinterposition between the blades 41 and 43 of the switch 13 thusresulting in such switch remaining closed when the drive camshaft I5 isin its switch actuating position shown in FIGS. 2 and 3, even thoughsuch cam bar 23 has been shifted to its cutoff position shown in FIG. 3.This assures that the blower will continue to operate thus pre ventingoverheating of the furnace heating elements even after the circuits tosuch elements have been opened as a result of opening of the remainingswitches 13.

The leads leading from the opposite end of the heat motor 72 may then beconnected in circuit with a thermostat sensing the temperature of theroom of which the temperature is to be controlled. The thermostaticlimit switch 37 may then be placed in the plenum chamber of the furnaceadjacent the heating elements, the overheating of which is to beprevented.

Thereafter, if the temperature of such room falls below the targettemperature, the thermostat will actuate to close the circuit throughthe heat motor 72 thus energizing such motor to heat the thermostaticcontrol rod 21 causing such rod to grow in length thus permitting thefree extremity of the secondary link 57 to rotate to the left as viewedin FIGS. 1 3 under the influence of the biasing spring 65 acting throughthe drive linkage 19. Such shifting to the left of the free extremity ofthe secondary link 57 permits the free extremity of the primary link 53to shift to the left thus shifting the drive camshaft 15 to the leftresulting in the respective cams 52 being moved out of alignment withthe respective switch blades 41 and 43 to permit such switch blades todraw inwardly toward one another on opposite sides of the necks 54 thuscarrying the electrical contacts 45 and 47 into engagement with oneanother. It will be appreciated that the staggered relationship of therespective cams 52 with respect to the respective blades 41 and 43causes the cams 52 on the left hand end of such camshaft 15 to firstclear the respective blades 41 and 43 to thus close the left-mostswitches 13 first. The remaining switches 13 are then sequentiallyclosed thus resulting in sequential energization of the control furnaceheating elements thus preventing placing the entire furnace loadinstantaneously on the power source to thus avoid overloading of suchpower source.

If during heating of the room the furnace malfunctions resulting inoverheating of the heating elements and raising the temperature of thelimit switch 37 above a selected level, such limit switch will be over--heated thus causing its thermostatic blade to warp to the position shownin FIG. 9 thus opening the circuit to the electromagnet 35 anddiscontinuing the magnetic attraction on the ferromagnetic keeper 33.Consequently, the upper extremity of the lever arm 27 will be drawncounter-clockwise under the influence of the biasing spring 29 to thusshift the cutoff camshaft 23 positively and rapidly to the left thusshifting the cutoff cam elements into alignment between the respectiveblades 41 and 43 of the respective switches 13 thus spreading the freeextremities of such blades apart to the position shown in FIG. 6 andseparating the contacts 45 and 47. It will be appreciated that the wedgeshaped slope of the respective cutoff cam elements 55 provides forwedging of such elements between the blades 41 and 43 to thus force suchblades apart and provide for the breaking of any relatively minorwelding that may have taken place between the contacts 45 and 47.

Referring to FIG. 9, it will be appreciated that the counter-clockwiserotation of the lever arm 27 resulted in opening of the reset switch 91thus de-energizing the heat motor 72 to permit cooling thereof resultingin shrinkage of the thermostatic rod 21 thus pivoting the free extremityof the primary lever arm 53 to the right and shifting the drive camshaft15 to the right, causing the right hand end thereof to engage thedownwardly extending flange 88 of the cutoff camshaft 23 thus shiftingsuch cutoff camshaft also to the right, it being appreciated that theshrinking of the thermostatic rod 21 (FIG. 1) provides sufficient forceto overcome the bias of the cutoff spring 29 and biasing spring 65.Thus, the keeper 33 will be reseated on the relay coil 35 and uponcooling of the limit switch 37, such coil will again be energized. Itwill be appreciated that the reset switch I 91 is not critical to thepresent invention and may be eliminated thus resulting in the cutoffdevice failing to reset itself and alerting responsible personnel thatthere has been a malfunction.

However, assuming the cutoff device 25 has been reset, if the thermostatcontinues to call for heat, the heat motor 72 will reheat thethermostatic rod 21 to thus shift the camshaft again to the left thusclosing the respective switches 13 and re-energizing the furnace heatingelements. If the malfunction has been corrected, the limit switch 37will not be heated above the normal temperature thus resulting in suchswitch remaining closed and avoiding reactuation of the cutoff device25.

From the foregoing, it will be apparent that the limit apparatus of thepresent invention provides an eco nomical and highly effective controldevice for controlling an electrical switch and for overriding thecontrol device to provide for positive opening thereof upon sensing of acutoff signal.

What is claimed is:

1. Limit apparatus comprising:

a housing;

electrical switch means mounted on said housing;

drive means coupled with said switch means;

control means connected with said drive means and operative in responseto a predetermined parameter exceeding a selected magnitude to actuatesaid drive means to open said switch means;

a cutoff device including a lever arm coupled with said switch means andcarried pivotally from said housing, said lever being shiftable from aninoperative position to a cutoff position to open said switch means,cutoff biasing means urging said lever to its cutoff position,ferromagnetic keeper means mounted on said lever arm, electromagneticmeans disposed adjacent said keeper means and operative uponenergization thereof to draw said lever arm against the force of saidbiasing means to said cutoff position; and

limit control means connected with said electromagnetic means andresponsive to a selected parameter to de-energize said electromagneticmeans whereby sensing of said predetermined parameter of said selectedmagnitude by said drive means will actuate said drive means to open saidswitch means and sensing of said selected parameter by said limitcontrol means will de-energize said electromagnetic means to cause saidbiasing means to shift said lever to its cutoff position.

2. Limit apparatus as set forth in claim 1 wherein:

said drive means includes drive cam means coupled with said switchmeans.

3. Limit apparatus as set forth in claim 1 wherein:

said cutoff device includes cutoff cam means engageable with said switchmeans.

4. Limit apparatus as set forth in claim 1 wherein:

said switch means includes a pair of substantially identical resilientblades mounted on their respective one ends from said housing andcontacts mounted on the free ends of said blades.

5. Limit apparatus as set forth in claim 1 wherein:

said switch means includes a plurality of controlled switches;

said drive means includes drive camshaft means formed with individualcams engageable with said respective controlled switches and shiftableaxially in one direction to a switch closed position to disengage saidcams from said respective switches for closing thereof and shiftable inthe opposite direction to a switch open position causing said switchesto open;

said cutoff device includes cutoff bar means coextensive with said drivecamshaft means and coupled with said lever arm, said cam bar means beingformed with individual cutoff cams engageable with said switches, saidcam bar means being ar ranged to be shifted axially in said onedirection when said lever is shifted to said cutoff position to engagesaid cutoff cams with said respective switches to open said switches.

6. Limit apparatus as set forth in claim 5 wherein:

said cutoff bar means includes flange means formed with an abutmentsurface projecting into the path of said drive camshaft means andengageable thereby as said drive camshaft means is shifted from itsswitch closed position to its switch open position to carry said cutoffbar means to its inoperative position; and

said control means includes drive biasing means coupled with said drivecamshaft means and having sufficient biasing force to overcome saidcutoff biasing means to enable said drive camshaft means to engage saidcutoff bar means and return said bar means to its inoperative position.

7. Limit apparatus as set forth in claim 5 wherein:

said cutoff means includes reset switch means connected in circuit withsaid control means and operative upon actuation of said cutoff device torender said control means inoperative.

8. Limit apparatus as set forth in claim 5 wherein:

said individual drive cams are arranged in staggered relationship withrespect to said switches to cause said controlled switches to be closedsequentially when said control means is actuated.

9. Limit apparatus as set forth in claim 8 wherein:

said respective cutoff cams are spaced apart a distance correspondingwith the spacing of said controlled switches to open said controlledswitches simultaneously upon actuation of said cutoff device.

10. Limit apparatus as set forth in claim 9 wherein:

said drive camshaft means and cutoff bar means are linear and projectparallel to one another.

1. Limit apparatus comprising: a housing; electrical switch meansmounted on said housing; drive means coupled with said switch means;control means connected with said drive means and operative in responseto a predetermined parameter exceeding a selected magnitude to actuatesaid drive means to open said switch means; a cutoff device including alever arm coupled with said switch means and carried pivotally from saidhousing, said lever being shiftable from an inoperative position to acutoff position to open said switch means, cutoff biasing means urgingsaid lever to its cutoff position, ferromagnetic keeper means mounted onsaid lever arm, electromagnetic means disposed adjacent said keepermeans and operative upon energization thereof to draw said lever armagainst the force of said biasing means to said cutoff position; andlimit control means connected with said electromagnetic means andresponsive to a selected parameter to de-energize said electromagneticmeans whereby sensing of said predetermined parameter of said selectedmagnitude by said drive means will actuate said drive means to open saidswitch means and sensing of said selected parameter by said limitcontrol means will deenergize said electromagnetic means to cause saidbiasing means to shift said lever to its cutoff position.
 2. Limitapparatus as set forth in claim 1 wherein: said drive means includesdrive cam means coupled with said switch means.
 3. Limit apparatus asset forth in claim 1 wherein: said cutoff device includes cutoff cammeans engageable with said switch means.
 4. Limit apparatus as set forthin claim 1 wherein: said switch means includes a pair of substantiallyidentical resilient blades mounted on their respective one ends fromsaid housing and contacts mounted on the free ends of said blades. 5.Limit apparatus as set forth in claim 1 wherein: said switch meansincludes a plurality of controlled switches; said drive means includesdrive camshaft means formed with individual cams engageable with saidrespective controlled switches and shiftable axially in one direction toa switch closed position to disengage said cams from said respectiveswitches for closing thereof and shiftable in the opposite direction toa switch open position causing said switches to open; said cutoff deviceincludes cutoff bar means coextensive with said drive camshaft means andcoupled with said lever arm, said cam bar means being formed withindividual cutoff cams engageable with said switches, said cam bar meansbeing arranged to be shifted axially in said one direction when saidlever is shifted to said cutoff position to engage said cutoff cams withsaid respective switches to open said switches.
 6. Limit apparatus asset forth in claim 5 wherein: said cutoff bar means includes flangemeans formed with an abutment surface projecting into the path of saiddrive camshaft means and engageable thereby as said drive camshaft meansis shifted from its switch closed position to its switch open positionto carry said cutoff bar means to its inoperative position; and saidcontrol means includes drive biasing means coupled with said drivecamshaft means and having sufficient biasing force to overcome saidcutoff biasing means to enable said drive camshaft means to engage saidcutoff bar means and return said bar means to its inoperative position.7. Limit apparatus as set forth in claim 5 wherein: said cutoff meansincludes reset switch means connected in circuit with said control meansand operative upon actuation of said cutoff device to render saidcontrol means inoperative.
 8. Limit apparatus as set forth in claim 5wherein: said individual drive cams are arranged in staggeredrelationship with respect to said switches to cause said controlledswitches to be closed sequentially when said control means is actuated.9. Limit apparatus as set forth in claim 8 wherein: said respectivecutoff cams are spaced apart a distance corresponding with the spacingof said controlled switches to open said controlled switchessimultaneously upon actuation of said cutoff device.
 10. Limit apparatusas set forth in claim 9 wherein: said drive camshaft means and cutoffbar means are linear and project parallel to one another.